Efficiencies can be realized for backup time and backup storage space by only storing copies of files that have changed since the last backup in the backup set. Modifications to a given file can be detected by comparing attributes or properties of the file including the last modification date and the file size. However, in some cases when an attribute or a property of a file (for example, a security setting) is changed, it does not change other attributes like the modification date and the file size. Also, in some cases an attribute or a property indicating a change has occurred is reset during the course of a first operation (for example, the archive bit is reset during or after a first backup), such that the change information intended to be represented and/or conveyed by attribute or property is lost once the first operation has been performed, making it unavailable to be used by a second, subsequent operation (for example, a second backup, e.g., to a different backup data set and/or storage location) to determine that the item has been changed. It would be useful in such cases to be able to detect and remember as long as needed that the files have changed, so that efficient incremental backups, including backups to two or more backup sets and/or destinations, can be performed.